The effects of four instrumentation techniques on root canal shape.

Recently, a new methodology was introduced for the study of root canal instrumentation. It has the advantages of using extracted human teeth in which original canal shapes can be compared with postinstrumented shapes. Four instrumentation techniques were compared for (a) their ability to maintain files in the center of the canals; (b) the amounts of dentin removed; (c) the directions and lengths of transportation; and (d) the final shapes of the instrumented canals. There was a trend for Flex-R files using the “balanced force” technique to remain centered in the canals. The result was not statistically different from that of a step-back technique, Flex-R files in an Enac ultrasonic system, or Zipperer files in the Enac system. There was less overall dentin removed with the step-back method. With all four techniques, the original canals were transported in the same directions at different canal levels. The majority of canals in the balanced force group were round whereas the majority in the other three groups were oval.